Archive for October 2010

The power of infrared imaging

October 26th, 2010 by Charles Xie
Figure 1. An IR image of a freshwater cup and a saltwater cup after an ice cube was added to each.
Will an ice cube melt faster in freshwater or saltwater? Why do we salt the road in water? How does an iceberg melt and how might it affect the ocean currents? All these curious questions are wonderful for students to explore. And they are very easy to do.

However, the science behind these questions are not that easy. To explain the results, we will probably need some reasoning at the molecular level, which is not at all easy for lower-grade students. But that is what we hope them to learn. These explorations require not only hands-on but also minds-on, which is why they are so great. 

Figure 2. An IR image take after four
minutes showing the convection in
the freshwater cup.
They are not obvious at first glance and often can be counterintuitive. If you search "ice melts slowly in saltwater" in Google, you can find a lot of discussions and debates. Many students and teachers were confused by what they observed in such a simple system as an ice cube floating in a cup of saltwater. Most of the discussions were, however, merely theoretical.

Had they had an IR camera, the thermodynamic processes would have been much more obvious. Figures 1-4 show a series of IR images taken to reveal what happened in the two cups after an ice cube was added.

Obviously, ice molt faster in freshwater because cold molten water can sink to the bottom and warmer water at the bottom is pushed to rise. This process, called convection, runs continuously to carry heat from the whole cup to melt the ice cube.

Figure 3. An IR image taken after
nine minutes showing the cooling
effect at the bottom as indicated by
the greenish halo.
In the case of saltwater, the cold water just sat at the top. The only explanation of this is that saltwater is denser so molten freshwater from the ice cube cannot sink, even if it is colder. Somehow, saltwater provides greater buoyancy.

Figure 4 shows that sixteen minutes later, the cold front still had not reached the bottom. This means that not only convection slowed down but also conduction was very slow.

Figure 4. 16 minutes later...
Recall our finding that a cup of saturated saltwater can spontaneously develop a temperature gradient from bottom up. This experiment provides a direct evidence that supports the theory that the temperature gradient can be created by the salinity. However, this evidence is not decisive, as the phenomenon reported here happens in an unsaturated solution whereas the small temperature gradient only exists in a saturated solution.

The puzzle still remains unsolved.

Which colors absorb more light energy?

October 25th, 2010 by Charles Xie
Figure 1. A page with some color
strips under a table lamp. Click the
image to enlarge it to see the details.
We all know black objects absorb more light energy than white ones. What about red, green, blue, and any other colors? With an infrared (IR) camera, this is very easy to figure out.

Print some strips in any color you want on a page, as shown in Figure 1. Put the page under a table lamp and let the light shine on it for 10 seconds. Then aim an IR camera at the paper. Figure 2 shows the results.

Figure 2. An IR image showing the
amount of light energy absorbed by
the color strips.
Obviously the black strip absorbed the most. But the red, blue, and green ones did not absorb much. Interestingly, the dark gray and purple ones absorbed absorbed more than I would imagine.

I have to admit that I didn't know how other colors absorb light energy before doing this experiment. With an IR camera, you can easily check it out just on your own like what I did--for any color and any comparison.

If you have heard that Steve Chu, our Energy Secretary, has been serious about painting our roofs with light colors and Mayor Michael Bloomberg has agreed to answer the call in New York City, you may find this little experiment worth your while--you may pick a color that does not absorb a lot of energy yet it will be more colorful than white.

Visualizing convection without using ink

October 24th, 2010 by Charles Xie
Figure 1. A top view of a floating ice cube.
If you have done a convection demo using a container of water and some ink, you may have had to change the water after each demo since the ink had diffused everywhere, which may make the convection pattern less easy to observe. Depending on the size of your container, that is some work to do and some water and ink to waste.

Here is a greener and better way to do it--using an infrared (IR) camera. An IR camera shows hot and cold (typically) in red and blue colors, which can be considered as "IR ink" that can be seen only through an IR camera. With the tool, all you can do is to add some ice cubes or hot water to a container of water every time you need to do a demo. There is no need to change the water.
Figure 2. A side view of a floating ice cube showing "cold fingers." 

One thing to notice is that you should not use a glass container--because it reflects off IR rays that will get into the image. A clear plastic one is the best as it does not reflect much and it allows you to observe what happens inside (if anything visible) with naked eyes.

Figure 3. A view from another side
showing the the cooling at the
Figure 4. An IR image after hot water was added to room temperature water in a container showing hot water tended to float atop.
Figure 5. An IR image of a fish tank showing a clear pattern of temperature stratification.

Salinity gradient vs. temperature gradient

October 22nd, 2010 by Charles Xie
Figure 1. The salinity gradient and 
temperature gradient observed in an
open cup of saturated saltwater.
This is the fifth follow-up of the blog article: "A perfect storm in a cup of salt water?This investigation focused on the relationship between the salinity gradient and the temperature gradient. Is the temperature gradient caused by the salinity gradient, or the other way around? Both arguments seem to make some sense. On the one hand, one can argue that the salinity gradient stops the convection. On the other hand, warmer water tends to dissolve more salt. So we are in a chicken-egg situation.

Let's do an experiment to explore a bit further. I prepared two cups of saturated saltwater. One open and the other sealed. I let them sit overnight and then checked the salinity and temperature distribution the next day using Vernier's salinity sensor and temperature sensor. I did this by moving the salinity sensor and the temperature sensor together up and down in the saltwater. Figure 1 shows the results for the open cup.

Figure 2. The salinity gradient and
temperature  gradient observed in
a closed cup of saturated saltwater.
Note: The measurement was done
shortly after removing the seal. 
Hence the results can be regarded
as approximately those of the
sealed cup as the gradients will
take a longer while to establ
To measure the data for the closed cup, I first removed the seal and then quickly did the measurement. Since the salinity and temperature gradient would take some time to readjust after the seal was removed, we can pretty much assume that the results I got approximately reflect what would have been measured if the seal had not been removed. Figure 2 shows the results.

 The comparison of the results shows that the salinity gradient is about the same for the open and closed cup--the bottom is about 1.3 ppt saltier than the top, but the temperature gradients are quite different--the open cup measured about three times as large as the closed cup (0.3°C vs. 0.1°C). 

Due to the evaporative cooling effect, the overall temperature of the open cup is at least 0.5°C lower than the closed one.

What do these results suggest? A weak temperature gradient may exist in a closed system that does not have the driving force of evaporative updraft.

What would it take to disprove Intelligent Design?

October 15th, 2010 by Paul Horwitz

Scientific theories differ from other belief systems in that they are testable; in other words, they can be disproved. Imagine reading, for instance, any of the following headlines:

  • “Modern Chicken Fossil Found Side By Side with Dinosaur Bones”
  • “Chimpanzee DNA Radically Different From Human”
  • “New Data Shows Earth Only 10,000 [or 100,000 or 10,000,000] Years Old”

What do you think would happen to the theory of Evolution if any of those things occurred (assuming, of course, that the observations were replicated and confirmed)? It would certainly have to be radically modified, and might have to be rejected entirely, because according to the theory it just can’t happen that chickens and dinosaurs ever co-existed. And if human and ape DNA were found to differ by more than a few percent it would be very difficult, if not impossible, to reconcile that with present-day views of how these creatures evolved (relatively recently, from a common ancestor). And if the earth were really “only” ten million years old (much less ten thousand!) there wouldn’t have been nearly enough time for living cells, much less human beings, to have evolved.

In contrast, can you think of any way to disprove the theory of Intelligent Design? I used to think I could. Why not, I thought, look for imperfections in the design, instances where certain creatures seem less than ideally designed for their purpose. (As it happens, there are many examples of such suboptimal design.) But that approach doesn’t work. All the inefficiencies can ever prove is that the designer “works in mysterious ways,” or has a different aesthetic from ours about such things. So what appear to be botched designs may tell us something about the designer but they do not discredit the theory of Intelligent Design itself.

Intelligent Design doesn’t make predictions–other than the trivial one that living creatures should look as though they were designed. But that’s not a prediction; it’s just an explanation for a set of observations. It’s kind of like saying “Lightning looks as though Thor is throwing thunderbolts at us, therefore that’s what it must be.”

The Thor model of lightning is unscientific not because it’s wrong but because it’s untestable. There is no way, short of looking around for Thor and not finding him (and he could, after all, be hiding somewhere), of checking out the theory. Like Intelligent Design, it makes no predictions and, therefore, cannot be disproved. In contrast, the theory that lightning is caused by electric currents, while considerably harder to understand and at first blush a lot less plausible than the Thor model, predicts, among other things, that if Benjamin Franklin flies that kite in a thunderstorm one more time he’s liable to get fried.

Science is all too often taught as though it were merely a collection of facts. What we should be teaching is the process by which we have come to trust those facts, what evidence backs them up, and, most important, what new information could get us to change our minds. We need to teach kids that the hallmark of every scientific theory is that in addition to explaining known data it makes predictions about data that hasn’t been seen yet. Which means that every scientific theory is in constant danger of being disproved if those predictions fail to come true.

Until the Intelligent Design proponents can point to some finding–anything!– that might in future cause them to revise or abandon their theory, that theory is no more scientific than the once widespread belief that the plague was God’s punishment for our sins. If we allow such theories to be treated as science we might as well go back to curing disease by whipping each other to atone for those sins.

Blind iPhone user can “see” colors for the first time

October 15th, 2010 by Chad Dorsey

iPhone for the blind. Stirring description by a blind person about the power of accessible media. My favorite part is his realization that, with an app called Color Identifier his iPhone can tell him verbally what colors he’s “seeing.” However, he mistakenly tries it for the first time in the dark:

I have never experienced this before in my life. I can see some light and color, but just in blurs, and objects don’t really have a color, just light sources. When I first tried it at three o’clock in the morning, I couldn’t figure out why it just reported black. After realizing that the screen curtain also disables the camera, I turned it off, but it still have very dark colors. Then I remembered that you actually need light to see, and it probably couldn’t see much at night. I thought about light sources, and my interview I did for Get Lamp.First, I saw one of my beautiful salt lamps in its various shades of orange, another with its pink and rose colors, and the third kind in glowing pink and red.. I felt stunned.

Inspires me to think much more about Universal Design and the importance of general accessibility. It’s also powerful to think about what technology can do to make the invisible visible for anyone in simple ways.

(via Daring Fireball.)

Surface computing on human skin and walls? Microsoft LightSpace brings augmented reality to a new dimension

October 14th, 2010 by Chad Dorsey

Microsoft is moving beyond one surface onto multiple surfaces now. With their LightSpace research project, they are tracking virtual objects as they move off a surface and onto users’ hands to be carried around the room. Projectors keep the virtual objects in sync with the real-world objects. So you can write a virtual note, carry it around, and “drop” it onto a wall. This is apparently made possible through the use of something called “depth cameras,” important for Microsoft’s Kinect gaming platform:

“Depth cameras (such as those from PrimeSense1, 3DV, and Canesta) are able to directly sense range to the nearest physical surface at each pixel location. They are unique in that they enable inexpensive real time 3D modeling of surface geometry, making some traditionally difficult computer vision problems easier. For example, with a depth camera it is trivial to composite a false background in a video conferencing application.

A white paper on LightSpace describes more.

(via ZDNet.)

Project Tuva: Free Feynman lectures, nicely augmented

October 13th, 2010 by Chad Dorsey

I met the amazing Shafeen Charania in San Diego as well, and in one of our discussions, he told me about a very cool project he was connected to in Microsoft’s Education Products division. Apparently, Bill Gates was so enchanted by Richard Feynman’s Messenger Series of lectures that he acquired the rights so they could be shared broadly. When he asked the Microsoft Research group what to do with them, they promptly created Project Tuva, a nifty annotation and information surround to accompany the videos. Richard Feynman lecturing on conservation laws

The Messenger Series contains five classic lectures on the laws of nature, and Project Tuva provides interactive transcripts, time-linked commentaries, and the ability to take notes pinned to specific timestamps. The notes even show up on a global timeline for each lecture, and can be exported as a separate commentary.

This is a very interesting way to re-experience these lectures, or to view for the first time. Either way, it’s one of the best ways to see a true genius explaining some of the most important ideas in science.

Visualizing vapor pressure lowering

October 12th, 2010 by Charles Xie
Figure 1. Two shallow plastic containers. The left one holds a lot of salt and the right one is plain water. A small amount of water was added to the left one.
This is the fourth followup of the blog article: "A perfect storm in a cup of salt water?" that started this journey of discovery.

The vapor pressure lowering is an effect that says the water vapor pressure above saltwater is lower than that above freshwater. This is more generally described by Raoult's Law, which states that the vapor pressure of an ideal solution depends on the vapor pressure of each chemical component and the mole fraction of the component present in the solution. Since the sodium and chlorine ions hardly evaporate, the vapor pressure above saltwater comes from the evaporation of water molecules.

The molecular mechanism behind the vapor pressure lowering is easy to understand--the ions stay in the way of water molecules and slow down the rate of their evaporation and, in the case of salt, they even act to attract the water molecules and prevent them from leaving the solution.

Figure 2. An IR image of the two shallow containers right after water was added to the salt one on the left.

Let's try to use infrared (IR) imaging to visualize this process. Prepare two plastic containers like the ones shown in Figure 1. Add plenty of salt to one of them and some water to the other. Then add some water to the salt one. Figure 2 shows an IR image just after water was added. The image shows that the system absorbed heat while salt was being dissolved.

Figure 3. An IR image after half an hour showing that the evaporative cooling effect of the saltwater container is weaker than the pure water one.
Let the containers sit for about half an hour and then take another IR image. Figure 3 shows the result. Interestingly, the colors reversed. Now, the saltwater container appears to be warmer than the pure water one.

Figure 4. An IR image after a few hours showing that the contrast of colors became greater.
Wait for a few hours and then come back to take an IR shot. Figure 4 shows that the temperature difference became greater.

How to interpret these results? There are two mechanisms that cause the temperature difference.

One is the vapor pressure lowering mentioned above. Using a Vernier relative humidity sensor, one can confirm that the humidity above the saltwater is lower than that above the freshwater. This means that the evaporation weakens above saltwater, which reduces the cooling effect.

The other is the crystallization of salt that releases heat. The evaporation of every water molecule weakens the ability of the solution to hold ions. As water constantly evaporates, a corresponding amount of ions must return to the crystalline form--mostly at the bottom because the contact area with the wall is much smaller compared with the contact area with the bottom. This process releases heat at the bottom. Since the saltwater is very shallow, the heat conduction may happen fast enough so that the crystallization heat will pass to the surface of the saltwater--even if convection may be insignificant with such a shallowness--and make it even warmer on top of the weaker evaporative cooling effect. This effect, which is totally based on molecular reasoning, is yet to be confirmed by an experimental method.

The vapor pressure lowering process and the crystallization process in this system are intertwined. If evaporation slows down (absorb less heat) due to salt, crystallization slows down (release less heat) too. The small amount of crystallization heat transfers to the surface and slightly increases the evaporation rate, which in turn causes slightly more ions to crystallize. The two processes manage to keep the saltwater container warmer than the freshwater container. But we still don't know which process contributes more. The question is, without the crystallization heat, can the IR image of the saltwater be as warm as it appears to be? How can we separate the two effects? Sealing the containers to stop evaporation doesn't work because that will stop crystallization as well.

Why do I insist on the theory of crystallization heat? Not only because it is logical. If we look at Figure 2, we will see that the effect of heat of solution is pretty significant. In order for salt to dissolve in water, some heat needs to be absorbed. Now, when the reverse process has to happen, i.e., when the salt ions have to return to the solid form, the same amount of heat must be released--in a much slower pace because of the low rate of evaporation (compared with the rate of dissolving). This is just simply the rule of energy conservation at work. The chemical potential must act like a spring. Energy is stored when it is "compressed" and released when it "bounces back."

Most likely, I now think this mysterious effect in a cup of saltwater is an orchestration of many physical and chemical effects. The salt gradient in a saturated solution is yet another mystery to be uncovered: the salinity gradient exists only in a saturated solution but not in any unsaturated solution.

A small cup of saltwater may contain a lot of physical chemistry! Stay tuned for more follow-up experiments.

Scientists measure relativistic effects at bicycling speeds

October 11th, 2010 by Chad Dorsey

They just measured relativistic effects between two atomic clocks differing by the speed of a fast bike rider and on length scales shorter than two feet.

Boy, this world is amazing.